The present specification relates generally to fabrication processes for integrated circuits. More specifically, the present specification relates to a system for and a method of using bacteria to aid in contact hole printing.
Semiconductor devices or integrated circuits (ICs) can include millions of devices, such as, transistors. Ultra-large scale integrated (ULSI) circuits can include complementary metal oxide semiconductor (CMOS) field effect transistors (FET). Despite,the ability of conventional systems and processes to fabricate millions of IC devices on an IC, there is still a need to decrease the size of IC device features, and, thus, increase the number of devices on an IC.
One limitation to achieving smaller sizes of IC device features is the capability of conventional lithography. In general, projection lithography refers to processes for pattern transfer between various media. According to conventional projection lithography a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film or coating, the photoresist. An exposing source of radiation (such as light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern.
Exposure of the coating through a photomask or reticle causes the image area to become selectively crosslinked and consequently either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble (i.e., uncrosslinked) or deprotected areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Projection lithography is a powerful and essential tool for microelectronics processing. As feature sizes are driven smaller and smaller, optical systems are approaching their limits caused by the wavelengths of the optical radiation.
One alternative to projection lithography is EUV lithography. EUV lithography reduces feature size of circuit elements by lithographically imaging them with radiation of a shorter wavelength. xe2x80x9cLongxe2x80x9d or xe2x80x9csoftxe2x80x9d x-rays (a.k.a, extreme ultraviolet (EUV)), wavelength range of lambda=50 to 700 angstroms are used in an effort to achieve smaller desired feature sizes.
In EUV lithography, EUV radiation can be projected onto a resonant-reflective reticle. The resonant-reflective reticle reflects a substantial portion of the EUV radiation which carries an IC pattern formed on the reticle to an all resonant-reflective imaging system (e.g., series of high precision mirrors). A demagnified image of the reticle pattern is projected onto a resist coated wafer. The entire reticle pattern is exposed onto the wafer by synchronously scanning the mask and the wafer (i.e., a step-and-scan exposure).
Although EUV lithography provides substantial advantages with respect to achieving high resolution patterning, errors may still result from the EUV lithography process. For instance, the reflective reticle employed in the EUV lithographic process is not completely reflective and consequently will absorb some of the EUV radiation. The absorbed EUV radiation results in heating of the reticle. As the reticle increases in temperature, mechanical distortion of the reticle may result due to thermal expansion of the reticle.
Both conventional projection and EUV lithographic processes are limited in their ability to print small features, such as, contacts, trenches, polysilicon lines or gate structures. As such, the critical dimensions of IC device features, and, thus, IC devices, are limited in how small they can be.
Thus, there is a need to pattern IC devices using non-conventional lithographic techniques. Further, there is a need to form smaller feature sizes, such as, contact holes. Yet further, there is a need to use bacteria to aid in contact hole printing.
The teachings here and below extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the above-mentioned needs.
An exemplary embodiment is related to a method of forming a contact hole having a critical dimension which is smaller than one minimum lithographic feature. This method can include providing a photoresist layer over a layer of material in which a contact hole is to be formed, etching the photoresist layer with an aperture having a first critical dimension, providing a bacteria film on the surface of the layer of photoresist which includes lateral side walls of the aperture, and etching a contact hole in the layer of material. The bacteria film decreases the aperture in width to a second critical dimension. The contact hole has the second critical dimension.
Another exemplary embodiment is related to a method of manufacturing an integrated circuit. This method can include patterning a standard feature size on a photoresist layer disposed over a substrate layer, providing for bacteria growth on the patterned photoresist layer where the bacteria growth forms a layer of bacteria along the top surface of the photoresist layer and side walls of the patterned features, and etching an aperture in the substrate layer according to the pattern defined by the pattern photoresist layer and the provided bacteria layer. The aperture has a critical dimension less than the standard feature size patterned on the photoresist layer.
Another embodiment is related to an integrated circuit having trench lines. The integrated circuit is manufactured by a method which can include patterning a standard feature size on a photoresist layer disposed over a substrate layer, providing for bacteria growth on the patterned photoresist layer where the bacteria growth forms a layer of bacteria along the top surface of the photoresist layer and side walls of the patterned features, and etching an aperture in the substrate layer according to the pattern defined by the pattern photoresist layer and the provided bacteria layer. The aperture has a critical dimension less than the standard feature size patterned on the photoresist layer.
Other principle features and advantages of the present invention will become apparent to those skilled in the art upon review of the following drawings, the detailed description, and the appended claims.